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            <h2 class="title" style="clear: both"><a id="persistobject"></a>Persistent Objects</h2>
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      <p>
                  When using the DPL, you store data in the underlying
                  DB databases by making objects
                  <span class="emphasis"><em>persistent</em></span>. You do this using Java
                  annotations that both identify the type of persistent
                  object you are declaring, as well as the primary and
                  secondary indices.
          </p>
      <p>
                  The following are the annotations you will use with your
                  DPL persistent classes:
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              <th>Annotation</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>@Entity</td>
              <td>
                                    Declares an entity class; that is, a class with a primary index
                                    and optionally one or more indices.
                            </td>
            </tr>
            <tr>
              <td>@Persistent</td>
              <td>
                                    Declares a persistent class; that is, a class used by an entity
                                    class. They do not have indices but instead are are stored or
                                    retrieved when an entity class makes direct use of them.
                            </td>
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              <td>@PrimaryKey</td>
              <td>
                                    Declares a specific data member in an entity class to be the
                                    primary key for that object. This annotation must be used one
                                    and only one time for every entity class.
                            </td>
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              <td>@SecondaryKey</td>
              <td>
                                    Declares a specific data member in an entity class to be a
                                    secondary key for that object. This annotation is optional, and
                                    can be used multiple times for an entity class.
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      <p>
                For example, the following is declared to be an entity class:
        </p>
      <pre class="programlisting">package persist.gettingStarted;

import com.sleepycat.persist.model.Entity;
import com.sleepycat.persist.model.PrimaryKey;

@Entity
public class ExampleEntity {

    // The primary key must be unique in the database.
    @PrimaryKey
    private String aPrimaryKey;

    @SecondaryKey(relate=MANY_TO_ONE)
    private String aSecondaryKey;

    ...

    // The remainder of the class' implementation is purposefully
    // omitted in the interest of brevity.

    ...
} </pre>
      <p>
            We discuss primary and secondary keys in more detail in <a class="xref" href="persist_index.html" title="Chapter 4. Working with Indices">Working with Indices</a>.
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